Memory array no common source region and method of fabricating the same

ABSTRACT

A memory array including a plurality of memory cells, a plurality of word lines, a dummy word line, and a plug is provided. Each word line is coupled to corresponding memory cells. A dummy word line is directly adjacent to an outmost word line of the plurality of word lines. The plug is located between the dummy word line and the outmost word line.

CROSS-REFERENCES TO RELATED APPLICATION

This is a divisional application of and claims the priority benefit ofU.S. application Ser. No. 13/045,153, filed on Mar. 10, 2011, U.S. Pat.No. 8,243,489 B2. The prior U.S. application Ser. No. 13/045,153 is acontinuation application of and claims the priority benefit of U.S.application Ser. No. 12/366,910, filed on Feb. 6, 2009, U.S. Pat. No.7,924,591. The entirety of each of the above-mentioned patentapplications is hereby incorporated by reference herein and made a partof this specification.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of and claims the priority benefit ofU.S. application Ser. No. 13/045,153, filed on Mar. 10, 2011. The priorU.S. application Ser. No. 13/045,153 is a continuation application ofand claims the priority benefit of U.S. application Ser. No. 12/366,910,filed on Feb. 6, 2009, U.S. Pat. No. 7,924,591. The entirety of each ofthe above-mentioned patent applications is hereby incorporated byreference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a semiconductor device and method offabricating the same. More particularly, the present invention relatesto a memory device and method of fabricating the same.

2. Description of Related Art

Non-volatile memory is currently used inside many types of electronicdevices for holding structural data, programming data and other randomlyaccess transient data. One type of non-volatile memory that can berepeatedly access is called flash memory. In fact, flash memory is anelectrically erasable programmable read only memory (EEPROM) device thatallows multiple data writing, reading and erasing operations. Inaddition, the stored data will be retained even after power to thedevice is removed. With these advantages, it has been broadly applied inpersonal computer and electronic equipment.

Conventionally, the memory device having a plurality of memory cellarranged in an array is constructed by several word lines parallel toeach other. Furthermore, as shown in FIG. 3, at the boundary of thememory region where the functional word lines 302 a are located, atleast one dummy word line 302 b is disposed directly aside thefunctional word lines 302 a for the purpose of increasing the exposureuniformity of the lithography process. However, the existence of thedummy word line 302 b aside the functional word lines 302 a in thememory region would lead to coupling effect between the dummy word line302 b and the nearest functional word line 302 a′. the coupling effectbetween the dummy word line 302 b and the nearest functional word line302 a′ leads to differentiating the performance of the nearestfunctional word line 302 a′ from the performance of other functionalword lines 302 a in the memory region. Therefore, the performances ofthe memory cells in the memory are not equivalent.

SUMMARY OF THE INVENTION

Accordingly, at least one objective of the present invention is toprovide a memory device structure capable of decreasing the couplingeffect between the dummy word line and the word line.

At least another objective of the present invention is to provide amemory device structure capable of overcoming the leakage during theprogram operation and the read operation.

A memory array including a plurality of memory cells, a plurality ofword lines, a dummy word line, and a plug is provided. Each word line iscoupled to corresponding memory cells. A dummy word line is directlyadjacent to an outmost word line of the plurality of word lines. Theplug is located between the dummy word line and the outmost word line.

A method of fabricating a memory array is further provided. A pluralityof memory cells is formed. A plurality of first plugs is formed. Aplurality of word lines and a dummy word line are formed. Each word lineis coupled to corresponding memory cells. The dummy word line isdirectly adjacent to an outmost word line of the plurality of wordlines. The step of forming a plurality of memory cells includes forminga plurality of first conductive regions disposed only on one side of thedummy word line, and the plurality of first plugs is located between thedummy word line and the outmost word line.

In the present invention, since the space between the dummy wordline/dummy gate structure and the nearest functional word line/stackedgate structure is enlarged and the shielding plug can be a metalshielding to isolate the nearest functional word line from being voltagecoupling with the dummy word line, the coupling effect between the dummyword line/dummy gate structure and the nearest functional wordline/stacked gate structure is decrease Therefore, the erase thresholdvoltage distribution of the memory cells in the memory device is tightenwithout being affected by the dummy word line. Furthermore, becausethere is no common source region/self-aligned source region around thedummy word line, the leakage problem during the read operation and theprogram operation can be overcome.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a top view showing a memory device according to a oneembodiment of the invention.

FIG. 2 is a cross-sectional view along line I-I in FIG. 1.

FIG. 3 is a top view showing a conventional memory device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a top view showing a memory device according to a oneembodiment of the invention. FIG. 2 is a cross-sectional view along lineI-I in FIG. 1. As shown in FIG. 1 and FIG. 2, a memory device 10 isprovided. In the memory device 10, a plurality of memory cells isarranged as an array. The memory cell can be, for example but notlimited to, a multi-level cell for storing multiple bit data. The memorydevice 10 mainly comprises a substrate 100. The substrate 100 can be,for example but not limited to, a silicon substrate with a firstconductive type. Alternatively, the substrate 100 can be a substratewith a shallow well (not shown) having the first conductive type.Moreover, a plurality of conductive lines 102 a disposed on thesubstrate 100 and the conductive lines 102 a are parallel to each other.The conductive lines 102 a can be, for example but not limited to, wordlines. It should be noticed that there are at least one semidetachedconductive line 102 b disposed aside the conductive lines 102 a. Also,the semidetached conductive line 102 b is disposed at a periphery of thegroup of the conductive lines 102 a. On the other words, thesemidetached conductive line 102 b is directly adjacent to the outmostconductive line of the plurality of the conductive lines 102 a. Thesemidetached conductive line 102 b can be, for example but not limitedto, dummy word line. Furthermore, the conductive lines 102 aelectrically couple to the memory cells respectively.

Moreover, each of the conductive lines 102 a comprises a data storageelement. The data storage element mentioned above can be, for examplebut not limited to, a floating gate or a charge trapping dielectriclayer. In one embodiment, as shown in FIG. 2, each of the conductivelines 102 a can be, for example but not limited to, a stacked gatestructure having a floating gate 104 and a control gate 106 located overthe floating gate 104. Also, the semidetached conductive line 102 b canbe formed together with the conductive lines 102 a. Accordingly, thesemidetached conductive line 102 b/dummy gate structure can be, forexample, the stacked gate structure as same as the conductive lines 102a. Further, the floating gate 104 is isolated from the substrate 100 bya tunneling dielectric layer 108 and is further isolated from thecontrol gate 106 by an inter-gate dielectric layer 110. The tunnelingdielectric layer 108 can be, for example but not limited to, made fromsilicon oxide by thermal oxidation. Also, the inter-gate dielectriclayer 110 can be, for example but not limited to, an oxide/nitride/oxidecomposite layer, an oxide/nitride composite layer or a silicon oxidelayer formed, for example, by carrying out a low-pressure chemical vapordeposition (LPCVD). Moreover, the floating gate 104 and the control gate106 can be, for example but not limited to, made from doped polysiliconby carrying out a chemical vapor deposition to form an undopedpolysilicon layer and implanting ions into the undoped polysiliconlayer. Alternatively, the floating gate 104 and the control gate 106 canbe fabricated in an in-situ ion doping and chemical vapor depositionprocess.

As shown in FIG. 2, a plurality of conductive regions 112 is disposed inthe substrate and between the conductive lines 102 a respectively andbetween the semidetached conductive line 102 b and the plurality of theconductive lines 102 a. Notably, the conductive regions 112 can bediffusion regions including several drain regions 114 and several sourceregion 116. Also, the drain regions 114 and the source regions 116 arealternatively arranged between the conductive lines 102. In addition,only one side of the semidetached conductive line 102 b in the substrate100 and between the semidetached conductive line 102 b and the pluralityof the conductive lines 102 a is arranged with one of the conductiveregions 112, which can be the drain region 114. Moreover, the conductiveregions 112 can be, for example, formed by implanting process. Morespecifically, the source regions 116 can be, for example, self-alignedsource regions. Additionally, the conductive regions 112 have a secondconductive type. The first conductive type is different from the secondconductive type. It should be noticed that none of the self-alignedsource regions 116 is arranged directly around the semidetachedconductive line 102 b.

As shown in FIG. 2, an inter-layer dielectric layer 118 is formed tocover the conductive lines 102 a, the semidetached conductive line 102 band the substrate 100. The inter-layer dielectric layer 118 isfabricated using borophosphosilicate glass (BPSG) or phosphosilicateglass (PSG) in a chemical vapor deposition, for example. The inter-layerdielectric layer 118 can further be, for example, planarized by backetching or performing a chemical-mechanical polishing process. Further,at least one shielding plug 120 penetrates through the inter-layerdielectric layer 118 and is located on the substrate 100. It should benoticed that the shielding plug 120 is immediately adjacent to thesemidetached conductive line 102 b and is located between thesemidetached conductive line 102 b and the plurality of conductive lines102 a. Moreover, the shielding plug 120 is electrically connected to theconductive region 114 located between the semidetached conductive line102 b and the group of the conductive lines 102 a. Also, the shieldingplug 120 can be, for example but not limited to, made of conductivematerial such as tungsten. In addition, there are several contact plugs122 located within the inter-layer dielectric layer 118 and electricallyconnected to the drain regions 114 between the conductive lines 102 arespectively. For example but not limited to, the shielding plug 120 canbe formed together with the contact plugs 122 in inter-layer dielectriclayer 118 at the same manufacturing step.

In the present invention, since the semidetached conductive line 102b/dummy gate structure is pull away from the nearest conductive line 102a by a shielding plug 120, the space between the semidetached conductiveline 102 b and the nearest conductive line 102 a is enlarged.Furthermore, the shielding plug 120 can be a metal shielding to isolatethe nearest conductive line 102 a from being voltage coupling with thesemidetached conductive line 102 b. Accordingly, the operationenvironments of the conductive lines are similar to each other and theperformances of the conductive lines are more equivalent.

Additionally, no self-aligned source region is disposed directly aroundthe semidetached conductive line 102 b. As shown in FIG. 1, it is clearthat the semidetached conductive line 102 b is separated from thenearest conductive line 102 a by the shielding plug 120 and there is noself-aligned source regions 116 directly around semidetached conductiveline 102 b, Accordingly, the coupling effect between the gate in thesemidetached conductive line 102 b and the gate in the nearestconductive line 102 a is decreased. Therefore, the erase thresholdvoltage of the conductive line close to the semidetached conductive linewould not be affected by the coupling effect. Thus, the erase thresholdvoltage distribution of the memory cells in the memory device will betighten.

Furthermore, because there is no source region, such as self-alignedsource region, directly around the semidetached conductive line 102 b,no current from self-aligned source region would leak through thesemidetached conductive line 102 b. Thus, the leakage problem during theread operation and the program operation of the memory device can beovercome. Therefore, the programming ability of the memory device isenhanced. Moreover, since the leakage of the memory cells in the memorydevices is suppressed and the erase threshold voltage distribution istighten, the read judgment window is enlarged.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing descriptions, it is intended that the presentinvention covers modifications and variations of this invention if theyfall within the scope of the following claims and their equivalents.

What is claimed is:
 1. A memory array, comprising: a plurality of memorycells; a plurality of word lines, each word line coupled tocorresponding memory cells; a dummy word line directly adjacent to anoutmost word line of the plurality of word lines; and a first pluglocated between the dummy word line and the outmost word line of thecorresponding memory cells, wherein no first conductive region isdisposed on one side of the dummy word line far from the outmost wordline.
 2. The memory array of claim 1, wherein the first conductiveregion is a source region.
 3. The memory array of claim 1 furthercomprising a plurality of second conductive regions disposed between theword lines.
 4. The memory array of claim 3, wherein the secondconductive regions comprise a plurality of drain regions and a pluralityof source regions and the drain regions and the source regions arealternatively arranged between the word lines.
 5. The memory array ofclaim 4 further comprising a plurality of second plugs located on theplurality of drain regions and electrically connected to the pluralityof drain regions.
 6. The memory array of claim 1, wherein a plurality ofdrain regions and a plurality of source regions are alternativelyarranged between the dummy word line and the plurality of word lines. 7.The memory array of claim 6, wherein the first plug located in one ofthe plurality of drain regions between the dummy word line and theoutmost word line of the corresponding memory cells.
 8. A method offabricating a memory array, comprising: forming a plurality of memorycells; forming a plurality of first plugs; and forming a plurality ofword lines and a dummy word line, each word line coupled tocorresponding memory cells and the dummy word line directly adjacent toan outmost word line of the plurality of word lines, wherein the step offorming a plurality of memory cells includes forming a plurality offirst conductive regions disposed only on one side of the dummy wordline, and the plurality of first plugs is located between the dummy wordline and the outmost word line, and no first conductive region is formedon one side of the dummy word line far from the outmost word line. 9.The memory array of claim 8, wherein the first conductive regions aresource regions.
 10. The method of claim 8 further comprising: forming aplurality of second conductive regions between the word lines.
 11. Themethod of claim 10, wherein the second conductive regions comprise aplurality of drain regions and a plurality of source regions and thedrain regions and the source regions are alternatively arranged betweenthe word lines.
 12. The method of claim 11 further comprising forming aplurality of second plugs on the drain regions and electricallyconnected to the drain regions.